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E-UTRAN Evolved UMTS Universal Mobile Telecommunication System Terrestrial Radio Access Network SAE System Architecture Evolution GAN Generic Access Network UMAN Unlicensed Mobile Acces

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Dear Reader:

Note that this book is primarily a training document because the primary business of INACON GmbH is the training and consulting market for mobile communications As such, we are proud to providing high-end training courses to many clients worldwide, among them operators like Cingular, Mobilkom Austria, SWISSCOM, T-MOBILE or VSNL (India) and equipment suppliers like ALCATEL-LUCENT, ERICSSON and SONY-ERICSSON, MOTOROLA, NOKIA-SIEMENS and RIM

INACON GmbH is not one of the old-fashioned publishers With respect to market, form-factor, homogeneous quality over all books and most importantly with respect to after-sales support, INACON GmbH is moving into a new direction Therefore, INACON GmbH does not leave you alone with your issues and this book but we offer you to contact the author directly through e-mail (inacon@inacon.de), if you have any questions All our authors are employees of INACON GmbH and all of them are proven experts in their area with usually many years of practical experience

time-to-The most important assets and features of the book in front of you are:

• Extreme degree of detailed information about a certain technology.

• Extensive and detailed index to allow instant access to information about virtually every parameter, timer and detail of this technology.

• Incorporation of several practical exercises.

• If applicable, incorporation of examples from our practical field experiences and real life recordings.

• References to the respective standards and recommendations on virtually every page.

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Sincerely,

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Table of Content

Assessment & Top Level View 1

1.1 Why is an Architecture Evolution necessary? 2

1.1.1 Integration of E-UTRAN with its new Concepts 3

1.1.2 Integration of Non-3GPP RAT's is sub-optimum in Rel 7 because 4

1.1.3 Therefore, legacy operators of Non-3GPP-RAT's cannot adopt the existing 3GPP-CN-Architecture 4

1.2 Important Requirements on SAE according to 3GPP 6

1.2.1 Coexistence 7

1.2.2 Service Continuation 8

1.2.3 Better Performance 8

1.2.4 Support of any Radio Access Technology (RAT) 11

1.2.5 Circuit-switched fallback 12

1.2.6 Management of Access Networks 12

1.2.1 Comprehension Check & Exercise: Reasons of a System Architecture Evolution? 14

1.3 Seamless Mobility Options and their Characteristics 16

1.3.1 Intra-RAT Mobility 17

1.3.2 Inter-RAT Mobility (w/o Optimizations) 18

1.3.3 Inter-RAT Mobility (with Optimizations) 18

1.4 Architecture Overview 20

1.4.1 Evolved Packet Core in Context 20

1.4.1.1 EPC vs EPS 20

1.4.1.2 Non-3GPP Access Networks (trusted / non-trusted) 21

1.4.2 Zoom into the EPS 22

1.4.2.1 Functional Overview of Core Network Elements within the EPC .23 1.4.3 Network Elements and their Functions within the EPC 24

1.4.3.1 Mobility Management Entity (MME) 24

1.4.3.1.1 Characteristics 24

1.4.3.1.2 Identification 24

1.4.3.1.3 Interfaces & Protocols 26

1.4.3.1.4 Tasks & Functions of the MME 28

1.4.3.1.4.1 NAS-Signaling towards the UE 28

1.4.3.1.4.2 S1-Signaling towards the eNodeB 28

1.4.3.1.4.3 S-GW and P-GW Selection 30

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1.4.3.2.4 Tasks & Functions of the S-GW 38

1.4.3.2.4.1 Packet Routing / Relaying 38

1.4.3.2.4.2 Legal Interception 38

1.4.3.2.4.3 QCI-based Packet Tagging 38

1.4.3.2.4.4 Accounting 38

1.4.3.3 PDN Gateway (P-GW or PDN-GW) 40

1.4.3.3.4 Tasks & Functions of the P-GW 44

1.4.3.3.4.1 UE IP Address Allocation 44

1.4.3.3.4.2 QCI-based Packet Tagging 44

1.4.3.3.4.3 Policy Enforcement 44

1.4.3.3.4.5 Home Agent Function 45

1.4.3.4 enhanced Packet Data Gateway (ePDG) 46

1.4.3.4.4 Tasks & Functions of the ePDG 50

1.4.3.4.4.1 ESP-Tunnel Mgmt towards UE's 50

1.4.3.4.4.2 QoS-specific Packet Tagging in UL-Direction 50

1.4.3.4.4.4 MAG-Function for PMIPv6 50

1.4.3.5 Protocol Stack Architecture on the UE-Side 52

1.4.4 Comprehension Check & Exercise: Interworking within the EPS-Architecture 54

Operations Overview 57

2.1 Network Access to the EPC in case of 3GPP-RAT's 58

2.1.1 E-UTRAN 58

2.1.1.1 Related Network Architecture 58

2.1.1.2 Related Network Elements 58

2.1.1.3 Signaling and Important State Changes (EMM, ECM, ESM) 60

2.1.2 GERAN / UTRAN 62

2.1.2.1.1 Selection of EPC vs GGSN 62

2.1.2.2 Signaling Procedures (GMM/PMM, SM) 64

2.1.1.4 Comprehension Check & Exercise: Relate E-UTRAN Procedures to GERAN / UTRAN Procedures 66

2.2 Network Access in case of Non-3GPP RAT's 68

2.2.1 Network Discovery and Selection 68

2.2.1.1 Problem Description 68

2.2.1.2 Interworking with the ANDSF 70

2.2.1.3 Distinction Trusted vs Non-Trusted Non-3GPP RAT's 72

2.2.2 Trusted Non-3GPP RAT's 74

2.2.2.2 Signaling Procedures if EAP and PMIPv6 are used 76

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2.2.3.3 Signaling Procedures if IKEv2 and DSMIPv6 are used 84

2.3 Voice Call Establishment 86

2.3.1 IMS-based 86

2.3.1.2 Signaling Procedure (SIP, SDP, DIAMETER) 88

2.3.2 Circuit-switched Fallback 90

2.3.2.2 Signaling Procedure for MOC 92

2.3.2.3 Comprehension Check & Exercise: Voice Call Establishment 94

2.4 Macro Mobility / Inter-RAT Roaming 96

2.4.1 Handover E-UTRAN to Trusted Non-3GPP RAT 96

2.4.1.2 Signaling Procedure (NBM / PMIPv6 on S2a) 98

2.4.2 Handover E-UTRAN to Non-Trusted Non-3GPP RAT 100

2.4.1.2 Signaling Procedure (NBM / PMIPv6 on S2b) 102

2.4.1.3 Comprehension Check & Exercise: Inter-RAT Mobility 104

Architectural Details of the EPS 107

3.0 Comprehension Test & Repetition: Network Interfaces and Protocols 108

3.1 Network Layout and Important Identifiers 114

3.1.1 Organization of the E-UTRAN 114

3.1.1.1 Tracking Areas 115

3.1.1.1.1 TAI and TAI-list 116

3.1.1.2 E-UTRAN Pool Areas 116

3.1.2 MME Pool's and MMEI 116

3.1.1.3 S-GW Service Areas 118

3.1.3 Identifiers of the UE 120

3.1.3.1 M-TMSI and S-TMSI 120

3.1.3.2 GUTI 122

3.2 Bearer Concept & QoS-Architecture in SAE 124

3.2.1 SAE-Bearers, Classification and Policy Enforcement 124

3.2.2 The QoS-Profile of the SAE-Bearer 126

3.2.2.1 GBR - Guaranteed Bit Rate 127

3.2.2.2 MBR - Maximum Bit Rate 127

3.2.2.3 AMBR - Aggregate Maximum Bit Rate 127

3.2.2.4 ARP - Allocation Retention Priority 127

3.2.2.5 QCI-Values and their Meanings 128

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3.2.3.6 OCS (Online Charging System) 132

3.2.3.7 OFCS (Offline Charging System) 132

3.2.4 Bearer Establishment & Authorization - Differences Rel 8 vs former Releases 134

3.2.5 Relationship and Dependency among the different Bearers 136

Protocol Suite 139

4.1 The “Mainstream” Protocol Stacks 140

4.1.1 Control Plane / E-UTRAN - EPC 140

4.1.2 User Plane E-UTRAN – EPC (S5/S8 GTP-based) 142

4.1.3 User Plane E-UTRAN – EPC (S5/S8 PMIPv6/GRE-based) 144

4.2 Generic Protocols within the EPC-Environment 146

4.2.1 IPv4 and IPv6 and their Differences 146

4.2.1.1 Headers and IP-Address Ranges 146

4.2.1.2 How to obtain an IP-Address 148

4.2.1.2.1 IPv4 and DHCP 148

4.2.1.2.2 IPv6 and “Stateless Autoconfiguration” 150

4.2.1.2.3 Real-Life Recording: Stateless Autoconfiguration 152

4.2.1.3 Fragmentation in IPv4 and IPv6 154

4.2.2 QoS in IP-Networks 156

4.2.2.1 DiffServ 156

4.2.2.1.1 Details of the AF(X,Y) PHB (Assured Forwarding) 158

4.2.2.1.2 Details of the EF PHB (Expedite Forwarding) 160

4.2.3 SCTP 162

4.2.3.1 Important SCTP-Functions 162

4.2.3.2 Example of an SCTP-Packet 164

4.2.4 DIAMETER 166

4.3 Protocols related to E-UTRA Networks 168

4.3.1 EPS Mobility Management (EMM) 168

4.3.1.1 Important EMM-Procedures 168

4.3.1.1.1 Common Procedures 169

4.3.1.1.2 Specific Procedures 169

4.3.1.1.3 Connection Management Procedures 169

4.3.1.2 State Machine 170

4.3.2 EPS Session Management (ESM) 172

4.3.2.1 Important ESM-Procedures 172

4.3.2.1.1 MME-initiated 173

4.3.2.1.2 UE-initiated 173

4.3.2.2 State Machine 174

4.3.3 Radio Resource Control RRC 176

4.3.3.1 Overview 176

4.3.3.1.1 Transmission of broadcast information 177

4.3.3.1.2 Establish and maintain services 177

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4.3.4 Packet Data Convergence Protocol (PDCP) 180

4.3.4.1 Overview 180

4.3.4.1.1 RoHC 180

4.3.4.1.2 Numbering of PDCP PDU’s 180

4.3.4.1.3 In-sequence delivery of PDU’s 180

4.3.4.1.4 Duplicate deletion 180

4.3.4.1.5 Encryption 181

4.3.4.1.6 Integrity Protection 181

4.3.4.2 Structure of PDCP PDU 182

4.3.5 The S1-AP Protocol 184

Call Flows & Scenarios 187

5.1 Attachment through E-UTRAN / new MME 188

5.2 Tracking Area Update 194

5.1.1 Inter MME tracking area update 194

5.1.2 Intra MME tracking area update 195

5.3 PDP Context Establishment 196

5.4 Inter MME Handover 200

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Chapter 1:

Assessment & Top Level View

Objectives

Some of your questions that will be answered during this session…

• Why is there a system architecture evolution in the first place?

• What are the requirements according to 3GPP?

• Is it possible to obtain just an overview of the new architecture?

• How will the protocol architecture of a typical UE look like?

• Which potential improvements are not covered by the SAE?

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1.1 Why is an Architecture Evolution necessary?

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The objective of this section is to point out why there is a system

architectural evolution necessary in the first place.

Consequentially, the offering of voice services over E-UTRAN is only possible as

VoIP This means a hard cut compared to previous 3GPP-technologies and

illustrates the reasoning behind the considerations of circuit-switched fallback

to be continued on the next page

• Abbreviations of this Section:

GERAN, UTRAN, )

E-UTRAN Evolved UMTS (Universal Mobile

Telecommunication System)

Terrestrial Radio Access Network

SAE System Architecture Evolution

GAN Generic Access Network UMAN Unlicensed Mobile Access Network

GERAN GSM EDGE Radio Access Network UTRAN UMTS (Universal Mobile

Telecommunication System) Terrestrial Radio Access Network

IP Internet Protocol (RFC 791) VoIP Voice over IP

LTE Long Term Evolution (of UMTS) WiMAX Worldwide Interoperability for

Microwave Access (IEEE 802.16)

QoS Quality of Service

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• Low Latency Requirements

• E-UTRAN imposes specific maximum latencies to be achieved for state changes within the E-UTRAN control plane (e.g from RRC-idle to RRC-connected) and, even more important, during the traversal of user data through the user plane

• In that respect, for the control plane state change latencies of app 50 ms are the target

• User data shall be delayed by no more than 5 ms in the ideal case when traversing through E-UTRAN Note that this value does not take into account latencies within the EPC or beyond!"Packet-switched only"

requires a serious QoS-integration with respect to e2e-integration and service differentiation

The full-scale integration of QoS is a precondition for the operation of any grade services over E-UTRAN If different services of the same or different users cannot be distinguished and differently treated, based e.g on their latency requirements, then E-UTRAN will probably fail

carrier-• Amendment of network controlled bearer management -> instead of managed only as in Rel 6

UE-This important change relieves the UE from the responsibility to request the establishment of real-time bearers and allows the network, esp the PCRF to take care of this function

1.1.2 Integration of Non-3GPP RAT's is sub-optimum in Rel 7 because

At the current time, the major difference between former approaches (Rel 6 ) and SAE with respect to macro-mobility, is the definition of so called optimized handover procedures for certain access network combinations (cdma2000 <=> E-UTRAN)

Without optimization, at the current time SAE pretty much relies on the capability

of the UE to operate two simultaneous radio links to enable seamless roaming between different access network types (e.g WiFi => cdma2000)

• In Rel 6 and 7, non-3GPP-RAT's are conceptually treated as "alien"

technologies to be amended to existing 3GPP-RAT's

There is no possibility in Rel 6 and 7 to consider specifics of foreign access networks when interconnecting them to a 3GPP-network Therefore, this interconnection is merely done on AAA-level with a transparent IPsec-tunnel between the UE and through that access network towards the 3GPP-network

1.1.3 Therefore, legacy operators of Non-3GPP-RAT's cannot adopt the existing 3GPP-CN-Architecture

• Which is very critical for those operators who want to adopt LTE / E-UTRAN

in addition to their already existing Non-3GPP-RAT's (e.g cdma2000 /

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• Which would be quite beneficial as 3GPP provides proven "off-the-shelf"

solutions

The number of 3GPP core networks exceeds by far any other implementation in

the market Their price and stability prospers quite a bit from the related volume

of scales effects

The other possibility has clearly been shown during recent years in the

WiMAX-area: The IEEE had only defined the air interface and therefore, a core network

and all protocols and procedures were missing It was finally the WiMAX-forum

that jumped in and filled out those gaps but it took years and a considerable

expenses which have to be settled among less shoulders

Room for your Notes:

AAA Authentication, Authorization and

Accounting PCRF Policy and Charging Rules Function (3GTS 23.203)

QoS Quality of Service

GERAN, UTRAN, )

EPC Evolved Packet Core (3GTS 23.401)

IEEE Institute of Electrical and Electronics

IPsec Internet Protocol / secure (RFC

LTE Long Term Evolution (of UMTS) UTRAN UMTS (Universal Mobile

OPEX Operational Expenditure WiFi Wireless Fidelity (www.wi-fi.org)

WiMAX Worldwide Interoperability for

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1.2 Important Requirements on SAE according to 3GPP

The objective of this section is to start the listing of requirements on SAE as stated by 3GPP.

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1.2.1 Coexistence

• With legacy architectures

We will illustrate that the SAE-core architecture is suited to interconnect to all

kinds of other network architectures

• Equal Support of IPv4and IPv6

The majority of the UE's will probably support both, IPv4 and IPv6

• Abbreviations of this Section: DL Downlink QoS Quality of Service E-UTRAN Evolved UMTS (Universal Mobile Telecommunication System) Terrestrial Radio Access Network RAT Radio Access Technology (e.g GERAN, UTRAN, )

GSM Global System for Mobile

I-WLAN Interworking WLAN (Wireless Local

Area Network) (3GTS 23.234) UE User Equipment

IPv4 Internet Protocol (version 4) UTRAN UMTS (Universal Mobile

IPv6 Internet Protocol (version 6) WLAN Wireless Local Area Network (IEEE

802.11)

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1.2.2 Service Continuation

The indicated interruption time appears to be rather high and unsuitable for time services

real-• Upon Change between circuit-switched and packet-switched radio access

This requirement relates particularly to the VCC feature as specified in 3GTS 23.206 and 3GTS 24.206

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• Abbreviations of this Section: 3GTR 3rd Generation Technical Report RAT Radio Access Technology (e.g GERAN, UTRAN, )

3GTS 3rd Generation Technical

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1.2 Important Requirements on SAE according to 3GPP

The objective of this section is to continue the listing of requirements on SAE

as stated by 3GPP.

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1.2.4 Support of any Radio Access Technology (RAT)

• Existing and future

• Trusted and non-trusted

This distinction is new with SAE whereas in prior releases every non-3GPP

access network was considered as “non-trusted” We will elaborate further later in

this book

3GPP Third Generation Partnership Project

(Collaboration between different

standardization organizations (e.g

ARIB, ETSI) to define advanced

mobile communications standards,

responsible for UMTS)

NSP Network Service Provider

ANDSF Access Network Discovery and

Selection Function (3GTS 24.302) RAT Radio Access Technology (e.g GERAN, UTRAN, )

BS Base Station (IEEE 802.16) SAE System Architecture Evolution

UTRAN UMTS (Universal Mobile

EPS Evolved Packet Switched WiMAX Worldwide Interoperability for

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1.2.5 Circuit-switched fallback

• In that case, the UE performs a combined attach through E-UTRAN to the EPC and the EPC updates the circuit-switched core network of the 2G/3G radio resources

• This way, the UE can remain reachable for incoming voice calls and will be paged

More details about the ANDSF will be provided later

• Access network sharing has been introduced to 3GPP with Rel 6 [3GTS 23.251] It enables a network operator to share their access network resources with other network operators who only need to deploy core network portions

• Which parts of the core network need to be deployed depends on whether the MOCN or GWCN configuration for access network sharing has been selected

• However, for the LTE/SAE-case, only the MOCN option makes sense and can be deployed

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3GPP Third Generation Partnership Project

(Collaboration between different

standardization organizations (e.g

ARIB, ETSI) to define advanced

mobile communications standards,

responsible for UMTS)

LTE Long Term Evolution (of UMTS)

3GTS 3rd Generation Technical

ANDSF Access Network Discovery and

Selection Function (3GTS 24.302) SAE System Architecture Evolution

UE User Equipment

(Rel 8 onwards) UTRAN UMTS (Universal Mobile Telecommunication System)

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1.2.1 Comprehension Check & Exercise:

Reasons of a System Architecture Evolution?

Question No 1: Please state the three most important characteristics of the envisaged system architecture compared to today's technology and architecture from your perspective

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1.3 Seamless Mobility Options and their Characteristics

The objectives of this section are to illustrate the different variations of mobility and how they are implemented as part of the SAE.

Key points of this section are that:

1 Which mobility options are supported by a UE is communicated through the UE mobility capabilities [3GTS 24.302 (8.2.1.1)].

2 Inter-RAT mobility involves a considerable transition and interruption time,

if there are no specific optimizations in place and if the UE cannot operate two radio links simultaneously.

Image Description

• The image depicts two overlapping rectangles, one red and the other one yellow

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• The area in the middle of both rectangles (joined area) indicates the special case

of optimized inter-RAT mobility procedures

[3GTS 23.402 (4.1.3)]

1.3.1 Intra-RAT Mobility

• Intra-RAT mobility is always provided through technology-specific procedures

• For instance, the GSM recommendations describe precisely the tasks of the

mobile station and the network to enable the seamless mobility of the mobile

station in idle and dedicated mode

• Intra-RAT mobility is frequently called micro-mobility.

DSMIPv6 Dual Stack Mobile IPv6 PMIPv6 Proxy Mobile IPv6 (RFC 5213)

RAT Radio Access Technology (e.g

GERAN, UTRAN, )

GERAN GSM EDGE Radio Access Network SAE System Architecture Evolution

NBM Network Based Mobility WiMAX Worldwide Interoperability for

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1.3.2 Inter-RAT Mobility (w/o Optimizations)

• Generically, inter-RAT mobility is frequently called macro-mobility This process relates to the change of the radio access technology e.g from WiFi to E-UTRAN

• Typically, inter-RAT mobility makes use of IP-based mobility techniques like CMIP or PMIP CMIP represents what is referred to as HBM in the image while PMIP relates to NBM

Irrespective of whether HBM or NBM is applied, it is always the UE in case of

inter-RAT mobility w/o optimizations that decides autonomously which RAT is

used and whether a switch of the RAT is applicable Therefore, the difference between NBM and HBM is that HBM requires additional protocols in the UE and NBM requires additional protocols in the EPC

• If the user shall experience interruption-free services during a change of the RAT w/o optimizations, then the UE must support the operation of two simultaneous radio links: One with the former RAT and one with the new RAT Only after the latter one has been successfully established, the old radio link may be released

1.3.3 Inter-RAT Mobility (with Optimizations)

• Optimizations always relate to additional specifications that govern mobility related information exchange between the UE and the network

• This information exchange typically only occurs while a radio link exists and relates to the transfer of measurement data and handover information

• Therefore, optimized inter-RAT mobility can only be specified individually between two specific access network types (e.g E-UTRAN <=> cdma2000 [3GTS 23.402 (9)] or GERAN <=> UTRAN)

• In our image we illustrated various different examples of optimized inter-RAT mobility options all of which can be found in the orange colored overlap between the yellow and the red rectangle

• Optimizations lead to a considerable reduction of the transition and disruption times during inter-RAT changes and, very importantly, they avoid that the UE is required to operate two simultaneous radio links if these interruption times shall

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PMIP Proxy Mobile IP

(Rel 8 onwards) RAT Radio Access Technology (e.g GERAN, UTRAN, )

GAN Generic Access Network SAE System Architecture Evolution

GERAN GSM EDGE Radio Access Network UE User Equipment

IP Internet Protocol (RFC 791) WiFi Wireless Fidelity (www.wi-fi.org)

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1.4 Architecture Overview

1.4.1 Evolved Packet Core in Context

The objective of this section is to depict the EPC as new network cloud in context to the legacy and new network clouds.

• The image is split into two parts: in the upper part, the image illustrates the legacy network parts and clouds which already exist with 3GPP Rel 6 and 7

• These network parts and clouds are illustrated in gray color

• In the lower part, the new network clouds with Rel 8 are depicted They have been colorized to provide for a better distinction from the legacy network clouds

• I-WLAN IP access from non-3GPP non-trusted access network may be achieved either directly (lower option) or through the packet-switched core network domain (upper option)

1.4.1.1 EPC vs EPS

The two terms EPC and EPS can be distinguished as illustrated:

• The EPC represents the core component of the EPS

• The EPS contains the EPC and the E-UTRAN (LTE) access network However, it does not contain the other access networks

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1.4.1.2 Non-3GPP Access Networks (trusted / non-trusted)

• In the legacy part (gray) the image illustrates the so called non-3GPP non trusted

access networks which have been supported by 3GPP-recommendations since

Rel 6

• New with Rel 8 and SAE are the so called trusted non-3GPP access networks

Those trusted non-3GPP access networks comply to an EPC-operator's security

requirements [3GTS 33.402 (4.2)] and are therefore granted direct access to the

EPC More details are provided in chapter 2

Whether a non-3GPP access network is trusted or untrusted is

1 either pre-configured in the UE or

2 the UE learns the trust relationship during EAP-AKA authentication through

that access network from its home-PLMN

3 Yet another option is that the selected access network does not at all support

EAP-AKA authentication in which case the UE determines that it camps on

an untrusted non-3GPP access network

The major difference for the UE with respect to the trust relationship of the selected

non-3GPP access network is that in "untrusted case" the UE must establish an

IPsec-tunnel through IKEv2 with an ePDG in the EPC [3GTS 33.402 (8)]

The illustrated IPsec-tunnel through the non-3GPP trusted access network is only

necessary in case the S2c-interface is used and it comes without interface name

AKA Authentication and key agreement

(3GTS 33.102) IKEv2 Internet Key Exchange protocol / version 2 (RFC 4306)

IPsec Internet Protocol / secure (RFC

4301)

EAP Extensible Authentication Protocol

EAP-AKA Extensible Authentication Protocol

method for 3rd generation

Authentication and Key Agreement

(RFC 4187)

PLMN Public Land Mobile Network

(Rel 8 onwards) SAE System Architecture Evolution

I-WLAN Interworking WLAN (Wireless Local

Area Network) (3GTS 23.234) UTRAN UMTS (Universal Mobile Telecommunication System)

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1.4.2 Zoom into the EPS

The objectives of this section are to:

1.Illustrate the inner structure of the EPC and the E-UTRAN.

2 Point out the "one-to-many" nature of the interconnections within the EPS.

• The image depicts another time the two network clouds EPC and E-UTRAN and illustrates the physical interconnections (black lines) of the various network elements to the two IP-backbone networks

[3GTS 23.401 (5.3.2)]

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1.4.2.1 Functional Overview of Core Network Elements within the EPC

• The MME or Mobility Management Entity takes care of various control plane

functions like mobility management and session management

• The S-GW or Serving Gateway is the peer of the MME within the user plane and

its functions evolve around packet data routing and forwarding

• The PDN-Gateway has similar functions as the Serving Gateway but it remains

the anchor during a packet data connection even if MME and S-GW It is feasible

to assume that GGSN's will typically be upgraded into PDN-GW's

S-GW and PDN-GW may easily be integrated into a single box in order to save

hardware and latency A combination of MME and S-GW is probably less appealing

because the MME is a very slim hardware box

• The ePDG is required to interconnect non-trusted non-3GPP networks to the

EPC Its functions evolve around tunnel termination towards the UE and the

non-trusted non-3GPP access network

MME Mobility Management Entity (3GTS

23.401) (Rel 8 onwards)

(Rel 8 onwards) PDN-GW Packet Data Network Gateway (part of EPC)

ePDG evolved Packet Data Gateway (3GTS

EPS Evolved Packet Switched S-GW Serving Gateway (3GTS 23.401)

IP Internet Protocol (RFC 791) UTRAN UMTS (Universal Mobile

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1.4.3 Network Elements and their Functions within the EPC

1.4.3.1 Mobility Management Entity (MME)

1.4.3.1.1 Characteristics

The objective of this section is to illustrate the most important characteristics

of the MME.

• The MME is a network element that takes care of control plane tasks

• The MME may physically be part of an SGSN or S-GW or it may be setup as a stand-alone network element

• MME's are typically organized in pool areas (S1Flex) to provide for load balancing among the MME's which belong to the same pool All eNodeB's which belong the related E-UTRAN pool areas shall have access to the MME's belonging to this MME-pool area(s)

[3GTS 23.002 (4.1.4.1), 3GTS 23.401 (4.4.2)]

1.4.3.1.2 Identification

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MMEGI MME Group Identity

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1.4.3.1.3 Interfaces & Protocols

The objectives of this section are to illustrate the MME, its interfaces towards other network elements and the protocol stacks used on these interfaces.

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DIAMETER Successor of the RADIUS protocol MME Mobility Management Entity (3GTS

E-UTRAN Evolved UMTS (Universal Mobile

MSC Mobile Services Switching Center

EIR Equipment Identity Register MSC-S MSC-Server

EMM EPS Mobility Management (3GTS

EPC Evolved Packet Core (3GTS

23.401) (Rel 8 onwards) SCTP Stream Control Transmission Protocol (RFC 2960)

ESM EPS Session Management (3GTS

GTP GPRS Tunneling Protocol (3GTS

GTP-C GTP Control Plane UDP User Datagram Protocol (RFC 768)

HSS Home Subscriber Server [3GTS

23.002] HSS replaces the HLR

with 3GPP Rel 5

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1.4.3.1.4 Tasks & Functions of the MME

1.4.3.1.4.1 NAS-Signaling towards the UE

The objective of this section is to illustrate the MME as peer of the eNodeB and the UE for different signaling tasks.

The MME and the UE use the physical resources of the LTE-Uu-interface and the S1-interface to exchange NAS-signaling [3GTS 24.301] which relates to EMM and ESM

1.4.3.1.4.2 S1-Signaling towards the eNodeB

• MME and eNodeB use the S1-AP-protocol for various tasks as stated in the image

[3GTS 36.413]

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Specification MME Mobility Management Entity (3GTS 23.401) (Rel 8 onwards)

EMM EPS Mobility Management (3GTS

ESM EPS Session Management (3GTS

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1.4.3.1.4.3 S-GW and P-GW Selection

The objective of this section is to illustrate the responsibility of the different network elements to select specific entities inside their pools to become responsible for a certain UE.

• Is is the eNodeB that selects the MME out of an MME-pool

• The selection of the S-GW is done based on O&M-constraints

Nevertheless, if the possibility is there to select an S-GW which is integrated with the selected P-GW, the MME shall prefer this choice

• The selection of the P-GW is either predefined through a decision of the HSS of the registering UE or the MME may apply route optimizing decisions, e.g by selecting a local P-GW in the V-PLMN in case of roaming

The aforementioned route optimization is frequently called local breakout

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1.4.3.1.4.4 Other Selection Functions

• In addition to the aforementioned selection functions the MME is also responsible

to select the new MME in case of a handover with MME-change

• Besides, the MME will select the SGSN in case of inter-RAT handovers to GSM

or UMTS, if the packet-switched core network in the 2G/3G-domain supports the

Specification RAT Radio Access Technology (e.g GERAN, UTRAN, )

HSS Home Subscriber Server [3GTS

23.002] HSS replaces the HLR with

3GPP Rel 5

UE User Equipment

23.401) (Rel 8 onwards) UMTS Universal Mobile Telecommunication System

O&M Operation and Maintenance V-PLMN Visited PLMN

PLMN Public Land Mobile Network

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